31st January 2017, 12:59 AM
Modified John Coker pads
AeroPac has been using John's style of pads for as long as I've been a member... 15+ years. For the past few years rockets have gotten bigger and the motors have gotten more powerful. I've noticed that our pads had a tendency to wiggle under high thrust flights. (out at BR there seems to be quit a few of these) # years ago I made up some pretty simple guy line systems for the pads. Guys either did not know we had them or where in a hurry to fly. This winter I brought home one of the pads to see what else cold be done to strengthen them. Below is John's original design. The mast bracket is made from 1/4" stainless steel. and the flexing/wiggle comes from the point where the mast bracket ends and it's bolted to the legs. Too back up some these pads have been improved many times by a couple of people over the years to what they are now.
My plane was to 'beef- up' the mast booms. This was accomplished by welding 3/8 x 3/4" SS flat bar turning the flat bar into more of "channel iron". This about maxed out my little welder her at home. Below is a photo of the 6 modified boom brackets. The first one was painted and the rest were left au naturel and adds some bling to our pretty beat up pads.
Also, we have several booms each with either 1515 or 1010 rails. To make rail swaps easier I added 1010 rails to the backside of the 1515 booms. This makes them more useful and easier to swap...just flip it over! It may even add some strength to the booms.
So now on to the reason for this thread. I volunteered to make 8 Modified Coker pads for a group I've been hanging out with lately. I don't plan on doing much writing from this point on. If my oldest son is up for it there might be a detailed set of plans of sorts at the end of this thread.
31st January 2017, 01:21 AM
so what's a good start on materials for 8 Coker style pads?
100' 3x3x 1/4 sq Al tube
120' 1.5 x 1.5 x 1/8 sq Al tube
12' 1 1/4 solid Al bar
17' 3" structural Al Channel
3 sq ft 1/4 Al plate
A bunch of rail stops, 2 dozen Galv foundation bolts (boom adjustment bolts)
and many more bolts not purchased yet.
Blast deflectors: For years AeroPac has used blast bolted to the rail. For years we have been repairing rails and blast deflectors ripped off either by just the thrust or a cato or two. Having the blast deflector mounted to the rail or even the pad itself does not make sense. It just adds to forces on the pad that you really don't want or need...while trying to get your rocket to go where you point it. For this year we are using 2x2' x 3/16 steel plates laid right on the ground. This should be the least amount of influence on the pad itself.
All the material (500#) is currently hanging from the rafters in my shop.
I have a cut list and hope to get all this cut up in the next few days. Of course it's suppose to start raining again tomorrow!
Last edited by tfish; 31st January 2017 at 01:24 AM.
31st January 2017, 03:42 AM
Looks like you're keeping plenty busy in retirement, Tony. I'll bring a couple rockets to XPRS that should be a good "wiggle" test for the new pads.
31st January 2017, 03:53 AM
Real blast deflectors (4-6 inch steel ells) really should start to be incorporated somehow, IMHO.
2nd February 2017, 01:30 PM
How would you keep them vertical? You really do not want them attached to the pad for reasons already discussed in this thread.
Originally Posted by numbo
I think your idea could be simplified using curved sheet steel on a steel frame. Basically sitting on the ground converting exhaust from vertical to horizontal. Likely need to be fixed to the ground.
2nd February 2017, 01:52 PM
Yeah, spike-down plates isn't a terrible idea. A bit more setup, but a bit of added stability. I'm picturing a tuning fork on the back of a slide.
14th February 2017, 05:29 AM
I'm about 2/3rds of the way done cutting out pieces. Below is 400# of aluminum and 350# of steel (blast deflectors) Cutting this produced about 7 gallons of "man glitter" -chips.
14th February 2017, 06:03 AM
That's a lot of cutting you've had going on Tony, hope you have a bandsaw? I like the idea of putting 1010 and 1515 rails back to back, I think I will do that with the new pad we are going to build.
14th February 2017, 04:43 PM
Chrisn, I think a band saw would take much more time. I cut all then tubing with a cheap garage sale Delta chop saw. Each cut took about 10 seconds. Switching back and forth between 90 and 45 degree cuts is very quick.
15th February 2017, 04:00 AM
Wow, that is a lot of pads, Tony!
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